Electric and pedal driven bicycle with solar charging

ABSTRACT

The invention relates to an electric propulsion system for a multi-wheeled vehicle including though not limited to a bicycle. The preferred embodiment consists of a standard street bicycle with multi-speed transmission, plus an electrical propulsion system and a solar charging apparatus. This preferred embodiment is normally powered by a combination of motor and pedals, coupled such that either or both may provide power at any time. The electrical propulsion system consists of: a) a DC electric motor, B) a plurality of batteries, C) a hand lever operating a throttle means, D) a throttle means which controls a battery switching circuit for altering the plurality of batteries into a parallel configuration for a lower voltage to facilitate regenerative charging at times, and into a series configuration at other times for a higher drive voltage for the motor, as well as controls a voltage regulating circuit which regulates voltage to the motor, E) a continuously variable automatic transmission which selects the correct ratio for conditions between a high and a low limit without intervention by the operator, as well as automatically regulates clutching friction, and F) A regenerative braking arrangement which converts forward momentum of bicycle and rider into a charging current for the plurality of batteries during braking or slowing. The solar apparatus consists of a plurality of solar cells mounted on a disc fitted outside the spokes on either or both sides of either or both wheels. A rotatable coupler conducts the solar charging current from the solar cells to the plurality of batteries.

BACKGROUND OF THE INVENTION

This invention relates to an electric propulsion system for amulti-wheeled vehicle including but not limited to a bicycle. Electricpowered vehicles are inherently cleaner and quieter than their gasolineand diesel powered counterparts, with no warm-up and potentially lessmaintenance required.

Electric powered bicycles are well known in the art at least as far backas the Humber electric bicycle of 1898. There have been many variationsover the years including the patents of Rudwick (U.S. Pat. No.4,280,581), Havener et al (U.S. Pat. No. 3,966,007), and McCulloch et al(U.S. Pat. No. 3,921,745).

Standard components of a typical electric bicycle include a bicycle, aconventional lead-acid battery, a DC elegtric motor, drive means formechanically connecting the motor with a front or rear wheel, and athrottle means for electrically connecting the battery with the motor.There is a invariably a provision whereby pedal and motor power may beprovided in combination to add range between recharges and improve speedand hill climbing ability. There is sometimes a regenerative brakingarrangement such that the motor acts as a generator when slowing orstopping to convert the forward momentum of the bicycle and rider into acharging current to restore energy to the battery.

Many difficulties and optimization problems have been noted in priorart. One of the major problems is that a conventional lead-acid batterystores only a small fraction of the energy contained in an equal weightof gasoline or diesel fuel. Although nickel-cadmium and other types ofalternate battery offer improved energy density, capacity has not yetapproached that of gasoline or diesel fuel and cost may be prohibitive.

A related problem is that an electric propulsion system invariablyinterferes wtih the normal pedaling and handling of a bicycle.Increasing the size of the battery from some base size likely increasesrange between recharges, but further hampers pedaling and handling.Speed and hill climbing ability may also be negatively affected.Decreasing the size of the battery from some base size likely improvespedaling and handling, though decreases range between recharges and mayaffect speed.

The Dc permanent magnet motor has been widely refernced as a powerful,efficient, yet low cost option. One disadvantage is that frequent ratiochanges are needed to stay within the 1,500 to 3,000 RPM window ofhighest power and efficiency of this motor, and simultaneous changingratios for both motor and pedals is too difficult for most operators.The single ratio used in most prior art compromises either speed orhill-climbing ability to an unacceptable extent, and a simple yet highlyefficient automatic transmission is lacking.

An electric motor of about 1/10 horsepower providing a top speed ofabout 11-14 mph on level ground has been cited as optimum. One reasonfor this selection is that air resistance against a bicycle and a riderincrease rapidly above about 12 mph, and efficiency likewise diminishes.Another reason is that by having power parity with the unmotored bicycle(the average rider also generates about 1/10 horsepower with normalpedaling), the electrical bicycle routes and otherwise function as aconventional bicycle.

Regenerative breaking can extend the range of the electric bicyclebetween recharges by a significant amount. However, a relatively highmotor RPM is generally needed to overcome the terminal voltage of thebattery before charging can begin. For example, of a 12 volt permanentmagnet motor and a 12-volt battery are used under a ratio under a ratiosuitable for level ground, there would be little charging (or braking)at speeds below about 8 mph, and the variable braking action for a slowor rapid decrease in speed would be lacking. These problems have beenpartially solved in prior art through a variety of devices, thoughprogress seems to have come at the expense of complexity.

Where a friction clutch is used, an increase in efficiency and adecrease in premature wear is gained if a clutching force proportinoalto the load applied can be provided. A relatively high amount offriction is needed on first starting, a medium amount when crossinglevel ground, and a low amount when going down hill, whereas a springtype clutch provides a constant clutching force regardless ofconditions.

One clutching solution noted in prior art entails mounting a motor anddrive roller on a hinged or slidable frame. As the drive roller swingsor slides into contact with the driven tire, the opposing rotationbetween drive roller and driven tire produces a "gripping" actionproportional to load applied. One serious flaw is that only a singleratio between the motor and the driven wheel is realized.

Better handling and increased safety result if the motor can bethrottled for a variety of power levels. The throttle means of mostprior art, whereby the motor is switched between ON and OFF, is verysub-optimal in this regard. Another throttle means of prior art, whichcauses a plurality of batteries to be switched into parallel or seriesconbinations for at least two discrete voltage levels, with the lowervoltage level also useful in regenerative braking, offers someimprovement over direct switching The rheostat or dropping resistors ofother yet other prior art offers additional or even continuous voltagelevels, though dissipates an unacceptable amount of power into heat.

The throttle means of still other prior art, which incorporates a DC toDC converter to regulate voltage to the motor through varying the dutycycle of the applied battery voltage, provides a continuously variablevoltage level at improved efficiency over a rheostat or droppingresistors. However, full battery voltage is never delivered at fullthrottle because of the presence of an in line semiconductor, complexityis relatively high, and efficiency remains decidedly below that ofdirect switching.

In summary, designing a practical electric propulsion system for abicycle has proven to be a formidable task. As evidenced by the absenceof rarity of electric powered bicycles in commercial production at thistime, an electric bicycle which effectively competes against other formsof transportation remains lacking.

SUMMARY OF THE INVENTION Electric and Pedal-Driven Bicycle with SolarCharging

Accordingly, it is the primary object of the present invention toovercome said problems and inefficiencies and provide a practicalelectric propulsion system with solar charging for a vehicle includingthough not limited to a bicycle. This propulsion system overcomeslimitations of prior art through optimization of standard components andincorporation of practical and novel concepts, and thereby allows therider to travel further and faster and with fewer complications.

A more specific object of the present invention is to incorporatedevices which reduce the size and weight of the electric battery neededfor a bicycle and rider to cover a given distance over the course of aday. One way this objective is accomplished is through a novelregenerative braking arrangement, which operates more effectively and atlower speeds than is possible with current art, is variable for more orless braking action, and effective to the extend that the need for aconventional rear friction brake is eliminated.

Another way this object is accomplished is by novel solar cellarrangement which recharges the batteries during daylight hours. Since abicycle is ordinarily used for a number of excursions over the course ofa few miles at a time, left idle for the remainder of the day, andridden only in clear weather, charging time while parked is sufficientto replenish energy to a major extent.

Another of the present invention's objects is to position the componentsof the electrical propulsion system so as to arrive at optimal weightdistribution and highest convenience to the operator. One way thisobjective is met is by mounting the plurality of batteries used in thisdesign so as to provide an optimum center of gravity and to minimizeinterference with peddling and maneuvering.

Still another of the present invention's objects is to provide a novelcontinuously variable automatic transmission capable of varying in ratiobetween an upper and a lower limit without the need for operatorintervention. The overall ratio between the upper and lower limits ofthis transmission is about 2.30:1, weight is only a few pounds, andruggedness is sufficiently for high dependability. This transmissionalso

Yet another object of the present invention is to provide a throttlemeans incorporating a battery switching circuit and a novel variablevoltage circuit. This battery switching circuit connects the pluralityof batteries into electrical parallel at times for a lower terminalvoltage for more effective charging when regeneratively braking, andinto electrical series at other times for a higher terminal voltage("raw" drive voltage) for driving the motor. The variable voltagecircuit regulates the raw drive voltage to the motor with no loss ofbattery voltage at full throttle, and with a conversion efficiency inthe range of 90 percent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall pictorial view of the right side of a bicycleconstructed in accordance with the present invention.

FIG. 2 is a pictorial side view of the left side of the bicycle showingthe motor and transmission of FIG. 1 as they are attached to thedowntube of the bicycle. FIG. 2 also shows how the motor andtransmission are coupled with gear sprockets, a chain, and a chaintensioner.

FIG. 3 is a sectional view as seen from above and behind thecontinuously variable automatic transmission employed in the bicycle ofFIG. 1. Included in FIG. 3 are the drive cone, spirally fluted driveshaft, return spring, swing axle, and associated hardware.

FIG. 4 is a pictorial schematic diagram of the battery switching portionof the throttle means employed in the bicycle of FIG. 1, showing theelectrical positioning of batteries and relays, the locations forrecharging the batteries, and the mechanical throttle control mechanism.

FIG. 5 is a simplified schematic diagram of the variable voltage circuitportion of the throttle means employed in the bicycle of FIG. 1. Thiscircuit takes the raw drive voltage delivered by the battery switchingcircuit, and regulates it into an infinite range of lower voltagelevels, as well as an equal voltage level, for delivery to the motor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In reference to FIG. 1, Batteries 2, 3, and 4 comprise 6-volt batteriesof the permanently sealed type so as to prevent leakage no matter howthe bicycle may be tilted. The 21/2-inch depth of batteries 2, 3, and 4allows each to be installed endwise for minimal interference withpeddling. In this preferred embodiment, batteries 2, 3, and 4 aresecured in battery frames 8 and 9 such that their combined center ofmass is in the vicinity of battery 3, thereby offsetting the inertia ofbattery 2 with that of battery 4 as the bicycle is turned duringoperation.

Circuit box 1 contains the battery switching circuit, the variablevoltage circuit, and the mechanical throttle control of the throttlemeans. One input to circuit box 1 is a throttle cable, similar to or thesame as the type used for a bicycle brake cable. The throttle leverwhich operates this throttle cable is mounted on the left side of thehandlebars, such that the operator can apply the throttle with the lefthand thereby leaving the right hand free for changing pedal gears.

Another input to circuit box 1 are conductive cables from each pole of6-volt batteries 2, 3, 4 (six cables in total) for use by the batteryswitching circuit. Battery combinations realized in this preferredembodiment are 6-volts when in parallel, and 18 -volt when in series.The output of circuit box 1 is a positive and negative power cable goingto motor 5. Motor 5, which is securely fastened to mounting frame 6 with"U" bolts, provides about 1/10 horsepower of output power. Mountingframe 6 is bolted to bicycle downtube 7.

Drive cone 10 clutches against tire 16 for ratio reduction andregenerative braking. Using tire 16 for these purposes reduces partscount, complexity, and weight of the present invention. Regenerativebraking is initiated as the operator actuates brake lever 12. The pullon this lever through a cable rotates lever 11, thereby forcing drivecone 10 firmly against tire 16 to prevent freewheeling and couple torquefrom the revolving wheel to motor 5.

Solar charging is provided by plurality of solar cells 13. Each unit ofplurality of solar cells 13 contains multiple individual solar cellssuch that about 7 volts of open circuit voltage is provided in directsunlight for charging the plurality of batteries through a blockingdiodes. This unit configuration maximizes charge in uneven light,whereas if all solar cells in the plurality of solar cells 13 wereconnected in series and light to one or more cells were to be disrupted,little charging would take place. Plurality of solar cells 13 provide oneach disc can contribute energy at the rate of about 25 watts in fullsunlight.

Plurality of solar cells 13 are mounted on disc 14, a disc which may beof the type commonly used to reduce friction between the spokes and thesurrounding air as the wheel rotates. In this preferred embodiment disc14 is rigidly attached to and outside of the spokes, though disc 14might also function as the spokes in supporting the weight of thebicycle and rider in some embodiments.

Disc 14 with plurality of solar cells 13 mounted thereon may be attachedon either or both sides of either or both wheels. Rotating ring andstationary brush arrangement 15 electrically connects plurality of solarcells 13 with batteries 2, 3, and 4 for charging, while at the same timeallows the wheel (s) to rotate freely.

FIG. 2 shows how motor 5 and the transmission of FIG. 1 are attached tomounting frame 6 and to bicycle downtube 7 as viewed from the left sideof the bicycle. Gear sprocket 17 is fitted to motor shaft 18, while gearsprocket 19 is fitted to spirally fluted transmission drive shaft 20,for a 1:1 gear ratio in this preferred embodiment. Drive chain 21interconnects gear sprocket 17 with gear sprocket 19. Gear sprockets 17and 19 normally rotate CW as viewed from this orientation, while tire 16normally rotates CCW.

Chain tensioner 22 both removes unwanted slack from drive chain 21, andurges drive cone 10 pivoting on swing axle 23 against tire 16, such thatthe outer periphery of drive cone 10 is in a constant friction contactwith the outer periphery of tire 16. Coil spring 24 provides force tourge chain tensioner 22 outwards and away from bicycle downtube 7.

FIG. 3 is a sectional view of the continuously variable automatictransmission such as might be seen from a rear luggage rack vantagepoint with motor 5 removed for unobscured viewing. Drive cone 10 ismachined from solid metal stock for a diameter of 13/4-inches at thelarge end, and 3/4-inches at the small end, for an overall ratio ofabout 2.3:1. The slope at the small end levels of a 1/2-inch wide step(as shown) for improved performance under high friction conditions.

A 5/16-inch hole bored longitudinally through drive cone 10 allowsspirally fluted drive shaft 20 to be inserted, while a 1-inch recess inthe large end of drive cone 10 allows a relatively long spring with amore linear compression tension to be used for return spring 25. Theopposite end of return spring 25 is abutted to keeper 27, which is inturn fastened to spirally fluted drive shaft 20.

Two 1/4-inch holes are bored and threaded on opposite sides of drivecone 10 within the 1/2-inch wide step of drive cone 10 as shown.Threaded set screws 26 are turned into the threaded holes such that thetip of each set screw extrudes into a recess formed by the spirallyfluted channels of spirally fluted drive shaft 20. These fluted channelscomplete about three and one-half complete revolutions over theirlength. As drive cone 10 slides to the left and right along spirallyfluted drive shaft 20, set screws 26 impart a rotating motion as theytrack inside the spirally fluted channels.

The transmission frame, which supports drive cone 10, spirally fluteddrive shaft 20, return spring 25, and associated hardware, consists ofbearing arms 29, crossmember 30, and brackets 31. Spirally fluted driveshaft 20 revolves in circular bearings 28, which serve to make alignmentof spirally fluted drive shaft 20 within this transmission frame lesscritical. Swing axle 23 allows the transmission frame to swing towardand away from tire 16. Swing axle 23 rotates on ball bearings 32contained within housing 33. Housing 33 is securely attached to mountingframe 6 with "U" bolts.

Lever 11 is essentially a cable-operated lever which, when activated,levers the transmission frame on swing axle 23 toward tire 16 for thepurpose of increasing friction between drive cone 10 and tire 16 forregenerative braking. Drive sprocket 19 is fitted to spirally fluteddrive shaft 20.

In operation, as drive cone 10 slides/rotates to the left, a smallerdiameter along its outer perimeter contacts an outer perimeter of tire16 and consequently a lower ratio with the driven wheel results. Asdrive cone 10 slides/rotates to the right, a larger diameter along itsouter perimeter contacts an outer perimeter of tire 16 and consequentlya higher ratio with the driven wheel results. With the 27-inch wheelused in this preferred embodiment, a highest ratio of about 1:15 isrealized as the large diameter end of drive cone 10 contacts tire 16,while a lowest ratio of about 1:36 is realized as the small diameter endof drive cone 10 contacts tire 16.

Drive cone 10 could be modified in a number of ways while staying withinthe intent of this disclosure. For example, drive cone 10 could have alinear overall slope of about 4:1 along its outer perimeter, alogarithmic slope, a "stepped" slope, etc.

As motor 5 turns spirally fluted drive shaft 20 through drive sprocket19, drive cone 10 positions to the left and right along spirally fluteddrive shaft 20 to provide the correct ratio between the shaft of motor 5and the driven wheel. Positioning of drive cone 10 is achieved as acompromise between torque provided by motor 5, which attempts to drawdrive cone 10 along the spirally fluted channels to the left and intolower ratios, and pressure provided by return spring 25, whichcontinuously urges drive cone 10 to the right and into higher ratios.

Upon first starting, high torque from motor 5 overpowers the urgingforce of return spring 25 and draws drive cone 10 to the left intolowest ratio. As motor 5 progressively comes up to about 1,500 RPM, theurging force of return spring 25 partially overcomes the medium torquefrom motor 5 and pushes drive cone 10 to the right and into mid-ratio.As motor 5 progressively comes up to about 3,000 RPM, the urging forcefrom return spring 25 overpowers the low torque produced by motor 5 andpushes drive cone 10 to the far right and into highest ratio.

The correct amount of friction between the perimeter of drive cone 10and the perimeter of tire 16 is also automatically adjusted as drivecone 10 moves to the left and right along spirally fluted drive shaft20. On first starting from a dead stop and with drive cone 10 movinginto leftmost position, the transmission frame swings toward tire 16into near right angle orientation. Friction is high in this orientationowing to a high level of "gripping" caused by the opposite rotation ofdrive cone 10 and tire 16. Drive cone 10 would actually turn over tire16 except for the presence of a built-in stop. The flat step machinedinto the small diameter end of drive cone 10 provides a more evensurface to improve performance under these high friction conditions.

As drive cone 10 moves into in mid-position, the transmission frameprogressively swings away from tire 16 into medium angle orientation.Friction is medium in this orientation, and results from a combinationof gripping caused by the opposite rotation of drive cone 10 and tire16, and pressure provided by chain tensioner 22. As drive cone 10 movesto the far right, the transmission frame progressively swings stillfarther away from tire 16 into low angle orientation. Friction is low inthis orientation, and results mainly from the pressure provided by chaintensioner 22.

As the operator releases the throttle, virtual freewheeling results astorque now provided by tire 16 counteracts most of the friction providedby chain tensioner 22, such that friction between drive cone 10 and tire16 is very low. A mechanism might also be incorporated to lift drivecone 10 off tire 16 for optimum freewheeling.

As the operator squeezes brake lever 12 to slow or stop the bicycle,lever 11 presses drive cone 10 firmly against tire 16. Freewheelingceases as tire 16 frictionally couples to motor 5 through drive cone 10.As the operator squeezes brake lever 12 yet more firmly, drive cone 10is pressed to the left on spirally fluted drive shaft 20 such that asmaller perimeter of drive cone 10 contacts tire 16, and braking actionincreases. A positive movement device to press drive cone 10 to the leftand into lower ratios with the wheel might also be incorporated into thedesign.

As depicted in FIG. 4, which shows the battery switching portion of thethrottle means, batteries 2, 3, and 4 can be charged by built-in (orexternal) battery charger 73, with ac input voltage applied acrosspoints 35. Batteries 2, 3, and 4 should be configured in parallel asthis charging occurs. The output of each unit of the plurality of solarcells 13 is applied between point 36 and ground, and charging ispossible whether batteries are configured in series or parallel. If inseries, any possible imbalance in charge between batteries 2, 3, and 4that might accumulate is equalized as batteries 2, 3, and 4 are onceagain configured in parallel.

Throttle mechanism 37 initiates action in both the battery switchingcircuit and the variable voltage circuit. With throttle mechanism 37completely closed, batteries 2, 3, and 4 are paralleled such that eachpositive pole is connected with all positive poles, and each negativepole is connected with all negative poles. The 6-volt terminal voltagewhich results allows charging current to more easily flow from motor 5when regeneratively braking.

As the operator first opens throttle mechanism 37, batteries 2, 3, and 4are connected into series such that the 18-volt raw drive voltageappears on conductor 50 as follows: Throttle cable 38 abutted tostationary point of bicycle frame 39 shortens while pulling againstreturn spring 40. Electrical contact 41 is grounded thereby groundingrelays 42, 45, and 48. As 6-volt dual-pole, dual throw relay 42 changesstate, its center taps 43 and 44 connect the positive pole of battery 2with the negative pole of battery 3, and 12-volts is thus seen at thepositive pole of battery 3.

As 12-volt dual-pole, dual throw relay 45 changes state, its center taps46 and 47 connect the positive pole of battery 3 with the negative poleof battery 4, and 18-volts is thus seen at the positive pole of battery4.

As 12-volt single-pole, single-throw relay 48 changes state, its centertap 49 makes the 18-volt raw drive voltage available to conductor 50.Delicate circuitry is thus protected from aberrant voltages that may bepresent during regenerative braking, and the possibility of leakagethrough motor 5 when the circuit is idle is eliminated. Regenerativecharging currents are routed through conductor 51.

As the operator further opens throttle mechanism 37, the ohmic valuebetween either end of the resistive portion of potentiometer 52 and thewiper is altered, though the sum of the resistances remains the same. Asthe operator opens throttle mechanism 37 still further, contact 53 isgrounded. As will be shown in FIG. 5, the shifting resistance valuesbetween either end of potentiometer 52 and the wiper and the groundingof contact 53 cause an increased voltage level to be applied to motor 5.

FIG. 5 is a simplified schematic diagram of the variable voltage circuitportion of the throttle means, which takes the 18-volt raw drive voltagedelivered over conductor 50 from the battery switching circuit, andreduces it to a continuum of lower voltage levels for delivery to motor5, ending with the full 18-volts.

Voltage levels less than 18-volts are achieved by rapidly connecting andthen disconnecting the 18-volt raw drive voltage to motor 5. Transistorsoperate most efficiently in either the full ON or fully OFF state, andhigh efficiency is thus achieved. For example, if the 18-volt raw drivevoltage is connected to motor 5 half the time over the duration of asecond (50% duty cycle), 9 volts would be effectively coupled. Theinductance present in the windings of motor 5 tends to smooth voltagefluctuations, as does the relatively high cycling rate.

Functional areas which comprise this variable voltage circuit are: 1)Three terminal voltage regulator 54, 2) R-S flip flop 55, 3) Sawtoothvoltage waveform generator 59, 4) "Window" comparator 65, and 5) Powerrelay 71.

Three terminal voltage regulator 54 is of the 12-volt type widelyavailable through electronic part retailers. Three terminal voltageregulator 54 takes the 18-volt raw drive voltage and reduces it to aregulated 12-volts for use by the delicate circuitry (but not motor 5).

R-S flip flop 55 essentially acts as a switch. The Q output of R-S flipFlop 55 is driven by its R and S inputs as defined by the "truth" tablewhich follows. When the Q output is high, driver transistor 56 enablespass transistor 57 to connect the 18-volt raw drive voltage to motor 5.When its Q output is low, pass transistor 57 is disabled and the 18-voltraw drive voltage is disconnected from motor 5. Diode 58 decouples passtransistor 57 from voltage spikes, and allows charging current to flowduring regenerative braking. Resistor 75 serves to limit current throughdriver transistor 56.

    ______________________________________                                        R              S           Q                                                  ______________________________________                                        low            low         no change                                          low            high        high                                               high           low         low                                                ______________________________________                                    

Sawtooth voltage waveform generator 59 and window comparator 65 form acontrol loop between the R and S inputs and the Q output of R-S flipflop 55 to establish duty cycle and cycling rate.

For sawtooth voltage waveform generator 59, the present state of the Qoutput is sensed and delivered to the + (positive) inputs of operationalamplifiers 60 and 61, which are configured as unity gain voltagefollowers. A high Q output drives the outputs of unity gain voltagefollowers 60 and 61 high, and since diode 62 is oriented to conductcurrent in the resultant polarity while diode 63 is not, unity gainvoltage follower 60 begins to charge timing capacitor 64 throughpotentiometer 52, while unity gain voltage follower 61 remains idle.Here a relatively low path resistance (as adjusted by the wiper ofpotentiometer 52) results in a relatively fast charge time of timingcapacitor 64, while a relatively high resistance results in a relativelyslow charge time of capacitor 64.

When the Q output of flip flop 55 is low, a low voltage level is routedto unity gain voltage followers 60 and 61. Both outputs are driven low,but since diode 63 is oriented to conduct current in the resultantpolarity while diode 62 is not, unity gain voltage follower 61 begins todischarge timing capacitor 64 through potentiometer 52, while unity gainvoltage follower 60 remains idle. Here a relatively low path resistance(as adjusted by the wiper of potentiometer 52) results in a relativelyfast discharge time of capacitor 64, while a relatively high resistanceresults in a relatively slow discharge time of capacitor 64.

The sum of the charge time and the discharge time of capacitor 64essentially remains a constant regardless of the wiper setting ofpotentiometer 52. As charge time increases, discharge timecorrespondingly decreases. The rising and falling voltage levels acrosstiming capacitor 64 constitute the sawtooth voltage waveform.

Next in the control loop, window comparator 65 takes the sawtoothvoltage waveform generated across timing capacitor 64 and generates theR and S logic levels to toggle the Q output of R-S flip flop 55 betweenhigh and low. Resistors 68, 69, and 70 form a voltage divider whichproportions the regulated 12-volts provided by three terminal voltageregulator 54 according to resistance values. Resistance values areselected such that the reference voltage at the upper end of resistor 69is a constant 8 volts (with respect to ground), while the referencevoltage at the lower end of resistor 69 is a constant 4 volts. Manyreference voltages are possible, though the chosen are a workablecombination.

Operational amplifier 66 is configured as a non-inverting comparatorwith its - (minus) input connected to the upper end of resistor 69, andthus referenced to a steady 8 volts, and its output is routed to the Sinput of R-S flip flop 55. Operational amplifier 67 is configured as aninverting comparator, with its + input connected to the lower end ofresistor 69 and thus referenced to a steady 4 volts, and its outputrouted to the R input of R-S flip flop 55.

The voltage level across timing capacitor 64 is sensed and delivered tothe + and - inputs of operational amplifiers 66 and 67 (respectively).First starting with a high Q output of R-S flip flop 55, the outputs ofcomparators 66 and 67 are both low as the voltage level across timingcapacitor 64 steadily rises. As this voltage level rises above 8 volts,the output of comparator 66 shifts to high. The logic combination thusexists at the R and S inputs of R-S flip flop 55 to toggle its Q outputto low. The output of comparator 66 shifts to low once again as the nowfalling voltage level coupled to its + input from timing capacitor 64falls below 8 volts.

As the now falling voltage across timing capacitor 64 decreases below 4volts, the output of comparator 67 shifts to high. The logic combinationthus exists at the R and S inputs of R-S flip flop 55 to toggle its Qoutput to high. The output of comparator 67 shifts to low once again asthe now rising voltage coupled to its - input from timing capacitor 64rises above 4 volts. The cycle repeats, with cycling rate mainly set bythe end-to-end resistance value of potentiometer 52 and the capacitancevalue of timing capacitor 64.

As the operator opens throttle mechanism 37 to maximum, relay contact 53is grounded and relay 71 is thus activated. As relay 71 changes state,its center tap 72 causes pass transistor 57 to be bypassed and the 18volt raw drive voltage on conductor 50 to be directly coupled with motor5, for full power and an efficiency of essentially 100 percent.

I claim:
 1. A D.C. power supply for providing a variable pulse widthmodulated voltage to one or more switching devices coupled to a load,the D.C. power supply comprising:sawtooth voltage waveform generationmeans for providing a sawtooth voltage waveform having variable rise andfall characteristics, said sawtooth voltage waveform generation meanscomprising first and second amplifiers, each having at least one inputterminal and an output terminal, the output terminal of said firstamplifier being connected to an anode terminal of a first diode, acathode terminal of said first diode being connected to a first terminalof an adjustable resistor, a second terminal of said adjustable resistorbeing connected to a cathode terminal of a second diode, and an anodeterminal of said second diode being connected to the output terminal ofsaid second amplifier, a variable resistance terminal of said adjustableresistor being connected through a timing capacitor to ground, thesawtooth voltage waveform being provided at the variable resistanceterminal of said adjustable resistor; a window comparator connected toreceive the sawtooth voltage waveform at the variable resistanceterminal of said adjustable resistor, said window comparator beingoperative for converting said sawtooth voltage waveform to a pair oflogic signals; an RS flip-flop coupled to the window comparator forreceiving said pair of logic signals and for controlling an on and offduty cycle of said one or more switching devices to apply a variablevoltage to the load; and a control loop coupling an output of said RSflip-flop to said at least one input terminal of said first and secondamplifiers for gating said sawtooth voltage waveform generation means.2. A D.C. power supply as in claim 1 wherein said adjustable resistorcomprises a potentiometer.